add denpendencyManagement in pom.xml
add "packing" element in gdm/pom.xml & ldm/pom.xml.

Signed-off-by: Samuel Deng <mr.dengshuoling@gmail.com>
add a "Core" Package to contains the main logic in LDM.
So, leave the Main.class outside of packge.

Signed-off-by: Samuel Deng <mr.dengshuoling@gmail.com>